In view of the increasing importance of polymers as substitutes for conventional materials of construction such as glass, metal, paper, and wood, the perceived need to conserve non-renewable resources such as petroleum and the dwindling amount of landfill capacity available for the disposal of waste products, considerable attention has been devoted in recent years to the problem of recovering, reclaiming, recycling or in some way reusing waste polymers. The disposal of thermoset polymers or resins is particularly challenging, since such polymers are highly cross-linked and hence do not melt or dissolve. In contrast, thermoplastic polymers such as polystyrene, polyethylene, polypropylene, polyamide, polybutylene terephthalate, polyethylene terephthalate, and the like may be readily liquefied by heating and the melted resin easily reshaped into useful articles such as films, fibers, injection or thermoform molded parts, and foamed sheets or containers.
It has also been proposed to pyrolyze or catalytically crack thermoplastic polymers so as to convert the high molecular weight polymer into volatile compounds having much lower molecular weight. The volatile compounds, depending on the process employed, may be either relatively high boiling liquid hydrocarbons useful as fuel oils or fuel oil supplements or light to medium boiling hydrocarbons useful as gasoline-type fuels or as chemical "building blocks." For example, polystyrene may be pyrolytically cracked s as to provide a substantial yield of styrene monomer.
However, the pyrolytic or catalytic cracking methods developed to date for use with thermoplastic polymers are not appropriate for use with thermoset polymers. For instance, U.S. Pat. No. 4,175,211 (Chen et al.) describes a process for converting relatively ash-free thermoplastic polymer wastes to liquid, solid, and gaseous products. The waste is mixed at a high temperature with a high-boiling refractory petroleum stream so as to preferably dissolve or melt the waste and the mixture then catalytically cracked. Thermosetting resins, according to the patent, cannot be successfully treated using such a process owing to the high resistance of these materials towards decomposition. The insolubility and infusibility of thermosetting resins in such petroleum streams will also interfere with the desired cracking process.
Yet another obstacle to the pyrolysis or cracking of a thermoset resin is the fact that such resins typically contain high proportions of various fillers such as glass fibers or inorganic powders (e.g., calcium carbonate, talc) to provide stiffness, strength, or reinforcement to the thermoset resin. Any method for reclaiming a thermoset resin must therefore provide an acceptable means of handling large quantities of insoluble, infusible and thermally stable filler. It would be highly desirable to recover the filler component from a waste thermoset polymer in a form such that it may be readily used again to reinforce a polymeric resin, since disposal of this component in a land fill or the like would not be environmentally or economically acceptable.